The present invention relates to a method for tensioning the chain of an internal combustion engine and to the related chain tensioner apparatus for performing the method.
In an internal combustion engine a continuous loop of chain is used for driving the camshafts of an engine from the output of its crankshaft. In order to compensate for any slackness in the chain that often occurs as a result of wear, a chain tensioner is used. Generally a chain tensioner comprises a hydraulic piston that is guided longitudinally in a bore of a housing and is biased into contact with the chain by meanes of the hydraulic pressure within the bore and/or a compression spring that acts between the piston and the housing. An end of the piston that projects from the housing is fitted with a shoe that rests on the chain to apply the appropriate tensioning force. When the piston is acted upon by the hydraulic pressure and/or spring force the chain is tensioned by the shoe. The hydraulic fluid also provides damping of the piston movement during use.
The hydraulic fluid in the chain tensioner is generally derived from the engine supply. The compression spring is designed to apply tension to the chain when the engine is off or during engine start up as at these times there is no or little hydraulic pressure. During normal operation of the engine the chain tensioner is tensioned by both the hydraulic pressure and the spring force. In most existing systems the chain tensioner is designed to ensure that sufficient tension is applied to accommodate all operating conditions and this results in the chain being over-tensioned for significant periods of it use. Maximum tension is required at engine start-up or at periods of rapid acceleration or deceleration when significant wear and noise can occur in taking up the slack of the chain, thereafter during normal use the chain is generally over-tensioned which itself contributes to noise and wear.
Mechanical tensioner that use only a spring force to bias the tensioning shoe are often used on belt systems offer constant tensioning loads that may be adequate for the start-up of the engine but which are over-compensatory when the engine is idling or operating at a constant speed.
In chain tensioner designs where hydraulic fluid is taken from the engine supply the pressure of the hydraulic fluid may increase with engine speed thereby increasing the tension of the chain unnecessarily. This increases the wear of the chain.
It will be appreciated that the problem with existing chain tensioners is that they are not responsive to the condition of the engine and are unable to apply a tension force that is variable in accordance with the requirements of the chain.
U.S. Pat. No. 5,159,904 describes a chain tightener system in which an electric control unit records one or more parameters of the operation of the engine and, in response effects a progressive and constant variation of the angular phase of rotation of the crankshaft and camshafts of an engine. This is achieved by using a pair of chain tighteners; one on the slack side of the chain and one on the tight side, However this arrangement cannot provide control over the chain noise, wear, vibration or harshness.
It is an object of the present invention to obviate or mitigate the aforesaid
According to a first aspect of the present invention there is provided a chain drive assembly for reducing noise, vibration or wear of a chain in an internal combustion engine, the assembly comprising a chain tensioner having a hydraulically actuated plunger for engaging a chain, the plunger being moveable within a housing and biasing means to bias the plunger outwards of its housing at least when there is no hydraulic pressure, means for controlling hydraulic pressure in the housing, means for measuring the projection of the plunger from the housing, means for measuring an operational parameter of the engine or drive assembly, means for calculating the desired chain tension in response to the measured operational parameter and means for transmitting a control signal to the chain tensioner so as to operate the biasing means or thee means for controlling the hydraulic pressure in the housing so as to control the projection of the plunger to apply the desired chain tension.
The achieve control of the chain tension not only reduces the noise etc. but provides for extended chain life.
The biasing means for controlling the projection of the plunger from the housing is preferably a solenoid, motor or a compression spring.
In one preferred embodiment the plunger is biased against a sliding member by actuation of the solenoid or motor. Hydraulic fluid may be supplied to the housing so as to act separately on the sliding member.
Preferably the desired chain tension is applied during operation of the chain.
The control signal may operate a control valve to control the flow of hydraulic fluid to the housing. The housing may have a plurality of chambers each receiving a different sized plunger member.
The operational parameter may be one or more of any of the following: the speed of r revolution of a crankshaft of the engine; the speed of revolution of at least one camshaft of the engine; the torque of the crankshaft; the torque of at least one of the camshafts; the relative phase of rotation of the crankshaft and at least one camshaft; the pressure of the hydraulic fluid in the chain tensioner; or the strain in the chain.
According to a second aspect of the present invention there is provided a method for tensioning the chain of a chain drive assembly so as to reducing noise, vibration or wear of the chain in an internal combustion engine, the drive assembly including a chain tensioner having a hydraulically, operated plunger that is moveable within a housing and biasing means to bias the plunger outwards of its housing at least when there is no hydraulic pressure, the method comprising the steps of measuring an operational parameter of the engine or drive assembly, measuring the projection of the plunger from the housing, calculating the desired chain tension in response to the measured operational parameter, transmitting a control signal to the chain tensioner so as to operate the biasing means or to change the hydraulic pressure in the housing so as to move the plunger to apply the desired chain tension.